TECH NEWS ///


T2 Lite: Impressive Mobile Video


/// By Davide Moro


Mobile TV reception is a recurring topic in digital broadcasting.


Almost every standard tried to hit the score with a specific set of parameters, and every “new” standard appearing on the market tries to raise the bar. T2 Lite, the mobile-oriented subset of the market-proven DVB-T2 standard, was approved in 2011. T2 Lite allows broadcasters to air specific mobile-targeted emissions, providing mobile signals with great robustness and high reception reliability, while delivering at the same time (and in the same channel) a fair amount of “classical” TV channels -- within about the same bandwidth that a DVB-T channel would use.


The R&D Department of RAI , the Italian public service broadcaster, has actively contributed to the standardization of the T2 Lite subset. They have been testing T2 Lite’s performance, even under severe reception conditions, since the very beginning.


In September 2011, a dedicated test bed at RAI R&D headquarter in Turin, Italy, proved the capability of T2 Lite to deliver TV content with excellent perceived quality – even at a S/N ratio equal to 1.5 dB. Yes, you read that right. RAI and its network operator


Rai Way are now broadcasting T2 Lite services within a DVB-T2 multiplex, through a simple SFN network set up in Aosta Valley. It is a mountain region in Northern Italy very well known for its ski resorts as well as for its challenging high mountain/narrow valley topography; at least according to RF specialists.


In late August 2013, I joined RAI R&D specialists for a comprehensive T2 Lite road test. If I were to use a single


//////////////// 6 TV Technology Europe I April 2014


word to describe my experience, it would be: Amazing. Anyway, let’s start from the


beginning.


T2-LITE IN BRIEF T2-Lite is the first DVB-T2 transmission profile that makes use of the FEF (Future Extension Frames) approach. It was intended to allow the inclusion of future technologies in the DVB-T2 standard. In this approach, some


frames in the DVB-T2 stream can be signalled as “unused,” and then be used to carry “different” signals. This way, first-generation DVB-T2 receivers will ignore them, while compatible receivers will be able to properly handle them; in some cases ignoring the “Base” DVB-T2 signals.


The T2 Lite subset includes


only elements relevant for mobile and portable reception, and the data rate is restricted to 4 Mbps per PLP. These features reduce the implementation complexity


TX Modulator and ETL DSCF2705


T2 Lite can deliver TV content with excellent perceived quality at a S/N ratio equal to 1.5 dB.


of the receiver’s chipset by 50 percent.


The FEF approach allows T2 Lite and T2 Base to be transmitted in one RF channel, even when the two profiles use different FFT sizes or guard intervals. FFT can be set to 32k for fixed-reception targeted T2 Base content (maximizing payload by reducing the guard interval); or to (say) 8k for T2 Lite content, allowing a wider carrier spacing and thus preventing Doppler effect issues when the receiver is moving at high speed. T2 Lite also features two


extra LDPC code rates. Time slicing is still supported at transport stream level. T2 Lite frames can be broadcast at pre- defined times only, and the receiver can be turned off during T2 Base frames to


preserve battery life in portable devices.


RAI R&D AND RAI WAY TRIAL The test network is based on a dedicated headend in the RAI facility in Aosta. A Harmonic re-multiplexer receives the national “Rai HD” programme from its “native” TS (to be aired in DVB-T standard) and multiplexes it with local content (generated in the same facility by RAI Regional Services) and with a 3D content loop-played from a local video server. These three channels are then included into the T2 Base PLP. The T2 Lite live content comes via SDI from the local production facility master control room. It is ingested through a Dektec DTU 2145 PCI adaptor, down-scaled in resolution to fit the typical


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